Storms led 737 overrun captain to opt against go-around

09 August, 2018

SOURCE: Flight Dashboard

BY: David Kaminski-Morrow

London

Pilots of a Boeing 737-400 freighter lost situational awareness and failed to realise how much runway had passed beneath the aircraft before a late touchdown which resulted in a high-speed overrun at Milan Bergamo.

The Hungarian-registered ASL Airlines aircraft had been conducting an ILS approach to runway 28 in poor weather and darkness on 5 August 2016.

While the crew had originally intended an approach with autoland, Italian investigation authority ANSV says they opted against autoland in favour of disengaging the autopilot and performing the landing manually.

Some 9nm from the runway the captain decided that, owing to the presence of storms on the missed approach pattern, he would not execute a go-around.

The first officer had logged just 86h on 737s, and told the inquiry that, while he was tempted to question this decision, he felt he did not have the experience to evaluate the situation and instead chose to trust the captain’s judgement.

But the first officer admitted to the inquiry that a go-around call “could have been a good idea”, given that the rain was intense and only the runway edge lights were visible. ANSV says this “poor assertiveness” from the first officer contributed to the accident.

Both pilots’ attention was focused, in the last moments of flight, on acquiring external visual references and they “did not realise” the aircraft had overflown the wet runway for 18s at high speed, the inquiry states.

For most of this passage the aircraft had been some 20-30ft above the runway, travelling some two-thirds of its length.

After touching down on the wet surface the jet was unable to decelerate sufficiently. It careered off the runway end, suffering extensive damage as it crossed roads and struck obstacles before coming to rest, having overrun by 520m.

ANSV says the crew did not monitor flight parameters adequately during the last stages of flight, and failed to disengage the autothrottle before landing. Although the captain had one hand on the thrust levers, the inquiry says that he did not recall that moving them would not disconnect the autothrottle.

Flight-data recorder analysis determined that the engine thrust reduced as the autothrottle transitioned to ‘retard’ mode, as designed, at a height of 27ft.

But engine thrust subsequently showed variations, increasing to as much as 97% N1, which the inquiry states were “presumably due to action by the crew”. This resulted in an increase in the landing speed, and the prolonged float of the aircraft, before it touched down at 159kt.

ANSV says that fatigue, while not perceived by the crew, could have contributed to the pilots’ decision-making processes. Both evacuated the aircraft but had suffered injuries during the accident and were subsequently hospitalised.